In vitro evaluation by DAPI staining of fresh, cooled and vitrified donkey embryos

The aim of this study was to evaluate the viability of fresh, cooled and vitrified donkey embryos by the 4’,6’-diamidino-2-phenylindole dihydrochloride (DAPI) staining method, was previously used for the evaluation of embryo damage (described as the percentage of dead per total cells) in the donkey species (Panzani et al. Theriogenology 2012;77:563–9). Eighteen 7 to 8 days old, quality I donkey embryos, recovered by uterine lavages with Ringer Lactate (RL), were divided in 3 groups: 1) Fresh (n=6, 7-days old; FR); 2) Cooled for 24 hours in a 5 ml test tube filled with the same RL recovered at the first uterine lavage (n=6, 8-days old; RL24); 3) Vitrified using the Equine Vitrification Kit (Bioniche Animal Health, USA) and the technique described for the horse (Eldridge-Panuska et al. Theriogenology 2005;63:1308–19) (n=6, 7-days old; VIT). After 24 hours of refrigeration in Equitainer® (RL24), after thawing (VIT) or directly after being recovered (FR), embryos were washed three times in Emcare Holding Solution (EHS), measured, moved for 5 min into EHS containing 1μg/mL DAPI and washed three more times in EHS. Dead embryonic cells (DAPI +) were directly counted under a fluorescence microscope, while the total cell number was estimated as described previously (n= 0.0106d2 + 2.0542 d – 375.28; n= cell number, d= embryo diameter in µm) (Moussa et al., Proc 20th Scientific Meeting of the IETS 2004;160). The proportion of DAPI stained cells was compared using One-Way ANOVA and LSD post-hoc test. The proportion of dead cells in the embryos of the 3 groups was lower than that reported to be the maximum limit for viability of horse embryos (Moussa et al. Theriogenology 2005;64:1619–32) in fresh embryos it was similar to that previously reported in donkeys (070.3 vs 0.91.17)(Panzani et al., 2011). The proportion of dead cells differed among groups (P<0.05): vitrified embryos were more damaged than fresh or refrigerated embryos (P<0.05). The transfer of fresh and vitrified donkey embryos was performed in previous studies and at 14 days resulted in pregnancy rates of 50% and of 36.4%, respectively, and to the birth of the first two live donkey foals after transfer of cryopreserved embryos (Panzani et al. J Equine Vet Sci 2012;32:419–9). The results of this study need to be extended with recipients’ pregnancy rates after transfer of a significant number of vitrified and refrigerated donkey embryos.